The Celts were an early Indo-European people who emerged around the 2nd millennium BCE and spread over much of Europe, ranging from the British Isles and northern Spain to areas as far east as Transylvania, the Black Sea coasts, and Anatolia in modern Turkey. They were not a single ethnic group but rather a collection of tribes sharing linguistic and cultural similarities, primarily identified by their use of Celtic languages. Their early culture is evidenced archaeologically starting with the Hallstatt culture (around 700 BCE) in Central Europe, followed by the La Tène culture, which spread westward and southward. The Celts were known as warrior-based societies living in clans within larger tribes. They inhabited areas including Britain, Ireland, western and central Europe, and parts of Anatolia. Their culture and language influenced many regions and some Celtic-speaking groups survive today in Ireland, Scotland, Wales, the Isle of Man, and Brittany. Historically, the Celts were documented by Greek and Roman writers, who referred to them with variations of the name "Keltoi" or "Celtae," but the Celts likely identified themselves by their specific tribes rather than a single collective name. In Britain, they arrived around 1000 BCE and lived through the Iron Age until the Roman invasion. Celtic tribes in Britain included the Britons and Picts, among others. Their society was based on farming, trading, and warfare, and their legacy continues through languages and cultural traditions in Celtic nations today. The Celts also had significant interactions and trade with Mediterranean civilizations like the Greeks and Etruscans. In summary, the Celts were a widespread and diverse group of ancient tribes united by language and culture, known for their warrior societies and influential Iron Age cultures in Europe.